Especially for the molding of thin-walled cups and similar articles, it is essential to insure an exact alignment of the core with a coacting cavity in the female mold portion. If the core is lightly tapered, the molded article adheres to it when the mold is opened and will therefore have to be stripped off by a ring closely hugging that core. Such a stripper ring, carried on a stripper plate extending radially beyond the mold, can also be used as a means for relatively centering the core and the cavity; injection molds have, in fact, been so constructed in the past.
This use of a stripper ring for centering purposes, however, subjects that ring to considerable wear which impairs its usefulness. If, instead, a locking ring of larger diameter is utilized for alignment purposes, the stripper ring is no longer radially accessible in the mold-closed position and must therefore be actuated by rods traversing both the male mold portion and the platen carrying that portion. Such a mounting is cumbersome and complicates the replacement of that mold portion by another.